1. Field of the Invention
This invention relates to apparatus for the calibration and alignment of pipe sections which are manufactured by automatic pipe making and cutting machinery and particularly to calibrating units having calibrating jaw means for calibrating the inside and outside dimensions of uniform length sections of pipe fed into the unit by means of feed rolls.
2. Description of the Prior Art
Pipe calibrating apparatus is known which comprises a central calibrating unit fed on one side thereof by feed rolls and connected on the other side thereof to a discharge device which delivers the calibrated pipe sections to delivery and storage. The feed rolls of the known device deliver 8 to 10 meter long pipe sections to the central calibrating unit wherein a pair of calibrating jaws close from an open position to make the measurement of the selected pipe sections. Calibration is recognized as an accepted and essential step in the manufacture of pipe because pipe sections are not straight but curved, to a greater and lesser degree, when received in the manufactured state and the straightening of the pipe, as received from production, has been a problem which the pipe industry has had to face to achieve the desired end of producing pipe in accurate tolerances for inside and outside diameters.
The requirements to approximate the ideal dimensions of roundness and diameter are particularly important in pipe which is to be used under high pressure conditions and especially in oil pipelines where thinned sections, or non-rounded sections, lead to conditions of overstrain and failure under high pressure conditions encountered in service.
To achieve the desired reliability, accuracy and efficiency in the known calibrating machines it has been found that one of the operating problems to be overcome is to compensate for nonalignment of successive pipe sections being calibrated in the central calibrating unit using calibrating jaws. Specifically the opening and closing movement of the jaws which occurs instantaneously upon encirclement of the pipe section by the jaws creates an overstrained condition and excess stresses in the pipe itself as well as in the calibrating jaws which surround the pipe. This overstrained condition results from excessive bending stresses and jaw contact pressures. In some instances the pressures are so excessive that the jaws and its mechanism are damaged.